Prior to the present invention there have been many types of temperature sensitive valves which include a fusible element so that when an excess temperature from a fire or other source is experienced by the valve, the fusible element melts and releases its support for the element of the valve, either the stem or other element, so that it can move to a fail safe position.
In U.S. Pat. No. 4,214,600 the valve stem is held in spaced relationship to the seat surrounding the bore through the bonnet so that when a fire occurs, the stem will move toward the seat and the shoulder on the stem will backseat to prevent leakage of fluids in the valve chamber out through the stem seals which are normally damaged during a fire.
U.S. Pat. No. 3,843,853 discloses another type of use for fusible material to hold a plunger in position on the top of a valve stem with a cap secured to the bonnet by a plurality of balls which are held in locked position by the plunger until the fusible material melts. At such time the plunger is allowed to be lifted a distance to cause an external groove to register with the balls and when the balls move inwardly into the external groove the cap and plunger are released and the valve stem is free to move to its fail safe position.
U.S. Pat. No. 4,271,857 discloses another type of valve wherein the fusible material provides the support to prevent the backseating of the stem during normal operations and also when it melts provides a bleeding of pressure from the actuator so that movement of the stem is not prevented by pressure locked in the actuator.
U.S. Pat. Nos. 4,421,134, 4,505,291 and 3,838,705 are all examples of different types of structures which include the use of a fusible material to allow some movement of the valve stem when it is exposed to a fire.
U.S. Pat. Nos. 3,651,823 and 3,744,506 are related patents and disclose a fail safe device for closing in an oil and gas well that has ignited. The device is connected to control the blowout preventer and includes two normally closed check valves which are spaced apart by an epoxy resin which prevents movement of pistons which hold the check valves apart but when the epoxy melts the check valves move together and unseat each other to provide a flow path through the device from the source of operating pressure fluid to the blowout preventer.